Soil conditioners promote cadmium reduction and selenium enrichment in rice: formulation process, effects, and mechanisms.

Excessive accumulation of cadmium (Cd) in rice from a selenium (Se)-enriched area is a global environmental issue. Due to its widespread presence and potential transfer through the food chain, it poses a significant threat to human health. Se, as an essential micronutrient for humans, reduces the Cd uptake of rice and mitigates the toxicity of Cd. The application of optimized soil conditioners has emerged as a promising agronomic strategy to mitigate Cd accumulation in rice grains while enhancing Se biofortification, leveraging the interactive mechanisms of Se-Cd antagonism in the soil-rice system. Based on the results of pot experiments, this study employed a uniform design method to optimize the formulation ratios of four materials. The results showed that soil conditioners have a significant positive impact on rice growth in Cd-contaminated soil. The application of soil conditioners could effectively reduce the available Cd concentration in slightly Cd-contaminated rice soils in a Se-enriched area of Jiangxi Province and regulate the enrichment coefficient and the transport coefficient of soil Cd and Se in various organs of rice. The theoretically optimal formulation predicted by the regression model was: lime, 1,500 kg hm-2; Ca-Mg-P fertilizer, 7,500 kg hm-2; and sodium humate, 870 kg hm-2. The experiment found that the T3 treatment was the most effective at inhibiting Cd accumulation and promoting Se accumulation. The formulation for the T3 treatment was: lime, 750 kg hm-2; Ca-Mg-P fertilizer, 6,000 kg hm-2; sodium humate, 4,500 kg hm-2; and zeolite, 0 kg hm-2. The application of T3 soil conditioner maximizes the reduction of Cd and increases the concentration of Se in rice grains, significantly enhancing rice yield. With the application of T3 soil conditioner, the estimate of the average soil available Cd concentration was 0.13 mg/kg. Compared with the control, the T3 soil conditioner reduced the available Cd concentrations by 43.4%. In addition, the T3 soil conditioner increased the available Se concentration by 0.0192 mg/kg compared with the control group. This enables high-yield cultivation of rice in Cd-polluted farmland with Se-enriched soil.